This invention relates to artifact reduction. In particular, scan line data is combined for reducing artifacts in contrast agent imaging.
Contrast agents, such as microspheres, are added into a patient to assist in medical diagnostic imaging. Contrast agents are sensitive to acoustic energies. Transmission of acoustic energy destroys or modifies the contrast agent. A loss of correlation due to changes of the contrast agent is determined and used to generate a medical diagnostic ultrasound image. In another method of detection, movement of the contrast agent without loss of correlation or in combination with some loss of correlation may be used to generate ultrasound images.
To determine the loss of correlation or movement of contrast agent, multiple beams of acoustic energy are transmitted along the same scan lines or to the same locations. Resulting echoes from the transmissions are sampled for determining the loss of correlation or movement.
Various transmit and associated energy sequences for a loss of correlation or motion detection imaging have been used. For example, a flow sample interleave ratio (FSIR) of 1 and a flow sample count (FSC) of 3 are used. As a result, three transmissions for three pulse repetition intervals are fired along each scan line before firing along another or adjacent line. For each scan line except the edge scan line for a region of an image, a pulse or energy sequence of eeeCCCeee is provided, where e represents energy from a transmit pulse along an adjacent scan line (i.e., e indicates energy at an edge of a transmit beam) and C represents energy from the transmit pulse centered along the transmit line of interest. Energy from transmit pulses along adjacent scan lines acts to destroy the contrast agent or cause collateral damage before transmissions for detecting movement or a loss of correlation sampling are fired. Where the collateral destruction or energy sequence is the same for each scan line, image artifacts may be avoided. However, where the energy sequence is different as a function of the scan line, image artifacts are created.
Receiving along multiple scan lines in response to a single transmit event may increase a frame rate. For example, in coherent contrast agent imaging, acoustic energy is received along two scan lines in response to a single transmit pulse or event. FIG. 1 represents a scanning sequence for a coherent contrast agent imaging process. In response to each transmit event, acoustic energy along two different scan lines is received. For each transmit event, the position of the transmitted energy and associated received focus is shifted. Acoustic energy along every scan line is subjected to the same collateral destruction and imaging destruction pattern: eCCe, avoiding contrast agent destruction artifacts. However, the process shown in FIG. 1 does not provide a level of sensitivity and agent specificity associated with the multiple pulse loss of correlation imaging methods described above.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below includes methods and systems for acquiring contrast agent data for imaging and for combining data representing different scan lines.
Line synthesis avoids artifacts from differences in collateral destruction of contrast agent. Data representing a plurality of scan lines is received in response to each transmit event. Transmission and reception along the same scan lines are repeated a plurality of times for loss correlation imaging. Coherent data or data prior to detection along two or more scan lines is combined, removing differences. The combined data represents a synthesized line of data for detection.
Line data representing contrast agents or not representing contrast agents may be synthesized from detected data. Detected data or data in the magnitude and phase domain representing two or more scan lines is combined. By altering the data provided to a flow processor or Doppler data detector, the relative phase of the data representing the two scan lines is determined. A magnitude for a synthetic line is calculated as a function of the magnitude of data representing two separate scan lines and the relative phase.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.